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Beards evolved to protect humans from a punch in the face

Lucy Goodchild van Hilten, 27th August 2020

Lucy Goodchild explores the findings and attention around a piece of research published in the previous month that caught the public’s attention. Listen to the accompanying podcast episode here.

Whether it’s a Van Dyke, a Hulihee or a full beard, facial hair appears to have enjoyed a resurgence in popularity in the last decade, with 42 percent of British men sporting facial hair by the end of 2016. But fashion aside, why do humans grow beards in the first place? What sort of biological benefit does it afford, if any?

This is a topic that Dr. David Carrier, comparative biomechanist and Professor of Biology at the University of Utah in the US, wanted to unpack – and he predicted a link with fighting. In a paper in Integrative Organismal Biology, Dr. Carrier and his team describe a study they conducted suggesting that beards may have evolved in humans to protect vulnerable bones during physical competition for mates.

Read the study: “Impact Protection Potential of Mammalian Hair: Testing the Pugilism Hypothesis for the Evolution of Human Facial Hair

To understand this research, we need to wind the clock back a couple of centuries. When Charles Darwin noticed that animals’ characteristics sometimes made sense for competing for mates but not necessarily for long-term survival, he developed the theory of sexual selection.

Connected to this is the observation that males and females of a species often have different characteristics, in terms of anatomy, physiology and behavior. This is referred to as sexual dimorphism. Dr. Carrier explained:

“Throughout the animal kingdom, females invest most in their offspring; that female investment is particularly pronounced in mammals, where you have females incubating the young in their bodies for a period of time followed by a period of lactation after they’re born. As a result, females tend to be picky about which males they mate with, and that puts males in the position of having to compete. In mammals, the primary competition in most species comes down to physical competition – the threat of a fight or an actual fight.”

Dr. David Carrier

This is where Dr. Carrier’s interest in beards comes in. Facial hair one example of sexual dimorphism in humans – generally, it’s the males that grow beards. This would suggest that beards play a role in sexual selection, that they give the males an advantage in competition with one another for mates.

 

Could beards protect humans in a fight?

Scientists have studied the role of facial hair in competition for mates; in fact, it’s something that Darwin looked at. Other species show sexual dimorphism in this area, like lions, elk and lynx, which have thicker hair around the neck region. In these cases, Darwin believed this was to protect the vulnerable neck area. But when it came to humans, his conclusion fell on the attraction side of the fence: that women are more attracted to men with beards.

Darwin’s conclusion may have been more readily supported by social observations in the 19th century, but today, it’s less apparent that females prefer full beards. Instead, Dr. Carrier and his team wondered whether beards provide some sort of protection to the face, connecting the sexual dimorphism in facial hair to physical competition for mates, like we see in other mammals.

The theory makes sense when you think about how humans fight, Dr. Carrier said. “If the desire is to actually kill another individual, we tend to show up with weapons. If the desire is just to control or manipulate another individual, then you’re going to get hand-to-hand fighting; in that physical combat situation, humans tend to use their fist, and the primary target when we strike is the face.”

A punch in the face is most likely to damage the jaw – epidemiological studies of emergency rooms show that the lower jaw is the most likely bone to break as a result of a punch. “We’re thinking that it may not be a coincidence that it is primarily the jaw that is covered by the beard,” Dr. Carrier said.

Dr. Carrier and his team wanted to test whether facial hair protects the facial bones. While they had used human cadavers in previous studies, it didn’t seem practical for this study, so they needed to develop a model that would behave in the same way as a human face. The model they came up with was a fiber epoxy composite for the jawbone, which has the same physical strength and toughness of bone, and sheep skin to mimic the skin and hair of the face.

An undergraduate student on the team built the models with skin that was shaven or unshaven on top of the fiber composite. Using something called a drop weight impact tester, they dropped weights on the model and measured the force of the impact.

“The results really surprised me,” Dr. Carrier said. “The forces were 16 percent greater when the fur wasn’t there, and about 40 percent more energy was absorbed when the fur was there.”

 

We like to read about ourselves

The surprising results go some way to explaining why the study attracted attention on social media and mainstream media, resulting in an Altmetric attention score of 595. The journal issued a press release, which led to the media coverage. Dr. Carrier believes it became popular for two reasons: it’s about humans, and it’s controversial.

“Any time you’re working on an unusual aspect of humans, people are going to have some interest in that for that reason, because it is about them,” he said.

Discover the coverage: https://oxfordjournals.altmetric.com/details/79862600/news

“We have not intended to draw attention, but I think it’s now at the point where we can predict. For example, we knew we knew this beard study was going to attract attention, even as we were starting it. We knew if we got anything interesting, there was going to be media attention.”

The beard study is the latest of many of the team’s studies that have caught the public’s attention. One reason for this is that in every case, the anatomy they study is also used for other things: for example, the proportions of the human hand enable us to form a fist to use as a club, but they’re also associated with manual dexterity. In this study, they are suggesting the beard provides an advantage by protecting the face, but another explanation is that it could be attractive to potential mates, which is what Darwin suggested.

“Some people find it incredulous that we would suggest that beards are somehow associated with fighting,” Dr. Carrier said. “From our perspective, it just follows that this incredibly sexually dimorphic character is associated with physical aggression. But there is some resistance to this idea that we may be anatomically specialized for fighting. It’s scary, because if it is true, it suggests that fighting has been important in our evolutionary past, that in some way we have become adapted to physical aggression. And if we’re anatomically specialized for aggression, well, maybe we’re behaviorally specialized for or in some cases inclined towards it.”

 

Prof. Carrier’s top tip for promoting research

“I’m not sure I have any specific advice other than an observation. Over the years, our work that has gotten the most attention has been the work that’s related to humans. The other thing that has tended to draw attention to this work is the controversial nature of it: the fact that it’s problematic for some people that we would be suggesting that part of the reason there may be facial hair in human males is that it provides protection in a fight. I think that controversy draws attention as well.”

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